Cu-NQR study of magnetism and superconductivity in Ce1+xCu2+ySi2 under pressure

In order to investigate the magnetic properties at the vicinity of magnetic to superconducting (SC) phase boundary, we have performed Cu-NQR measureme nts under hydrostatic pressure (P) on two off-stoichiometric CC1+xCU2+ySi2 Ce(0.99)Cn(2.02)Si(2) exhibits the anomalous ground state so-called A-phase , dominated by critical magnetic correlations and affected by a presence of minor SC fraction at ambient P. With increasing P which enhances the Kondo temperature the fraction of the A-phase is markedly suppressed, but the SC fraction is increased, although T-c stays nearly constant in the range of 1 bar <P<14.4 kbar. This evidences that the P-induced A- to SC phase change is of first order. In Ce0.975Cu2Si2 which undergoes a static magnetic orde ring (SMO) at ambient P below T-N similar to 0.6 K, no superconductivity ha s been induced up to 19.4 kbar. (C) 2000 Elsevier Science B.V. All rights r eserved.